Amorphous silicate minerals, often described as rock flour, were once common in natural water sources and abundant in glacial stream waters. Not only do the silica mineral particles bond water and other elements for transport; they also can be adsorbed with reduced hydrogen, which releases electrons, providing antioxidant or reducing potential to surrounding fluids. The purpose of this investigation was to examine the cardiovascular responses during exercise after consumption of a dietary silicate mineral antioxidant supplement, Microhydrin((R)) (Royal BodyCare, Inc., Irving, TX). A clinical trial incorporating a double-blind, placebo-controlled, crossover experimental design was employed. Subjects received either active agent or placebo, four capsules per day, for 7 days before the trial. The trial evaluated six exercise bicycle-trained subjects performing a 40-km bicycling time trial. Ratings of perceived exertion and measurements of oxygen uptake, heart rate, performance workload, and preexercise and postexercise blood lactate concentrations were obtained. Although there were no differences (P >/=.05) in work performed, heart rate, oxygen uptake, and ratings of perceived exertion during the time trial, the postexercise blood lactate concentrations were significantly lower (P </=.05) when the silicate mineral supplement was used, compared with placebo. These data suggest a beneficial effect of Microhydrin on lactate metabolism.